Prior art loss-in-weight feeders suffer from a loss in feed rate accuracy during the refill cycle. This is believed to be caused primarily by material compaction in the feeder hopper as material is added to the hopper.
In a typical prior art loss-in-weight feeder, material having known density is introduced at a relatively rapid rate into the feeder hopper. The material is then exhausted from the hopper at a much slower rate. The period during which material is introduced into the hopper is referred to hereafter as "refill" or "refill cycle". The period during which material is exhausted from the hopper is referred to as "discharge" or "discharge cycle". A feed screw located at the bottom of the hopper is rotated at a speed so as to deliver material at a desired flow rate. At the very beginning of the refill cycle, when very little material is in the hopper, the mass flow rate will be correct since the density of material within the hopper will be within expected limits. As material is added to the hopper, the material near the bottom of the hopper compacts. This increases the effective material density, and the mass flow rate increases, producing a flow rate error.